This invention relates to a transmission-type liquid crystal display element which is formed by injecting a liquid crystal between a pair of transparent plates and displays picture information by the electro-optic effect of this liquid, and to a liquid crystal display using this transmission-type liquid crystal element as a light valve.
The twisted-nematic (TN)-type liquid display element as a typical example of the liquid crystal display element has a liquid crystal cell formed of a liquid crystal injected between a pair of transparent plates with transparent electrodes, and two polarizers which are disposed before and after this liquid crystal cell so that their polarizing directions are 90.degree. different. The amount of transmitted light of the incident light is controlled to display picture information by the combination of the polarizing plane rotating action of the electrooptical effect of the liquid crystal and the polarizing component selecting action of the polarizers. The liquid crystal display element is described in detail in, for example, "Fundamentals and Application of Liquid Crystal Electronics" edited by Sasaki and published by a Japanese company, Ohm Company (1979). There are known further three prior arts "Integrated Planar Micro Lens and its Applications" Proc. Soc. Photo. Opt. Instrum. Eng., 898, 3-11 (1988); U.S. Pat. No. 5,052,783; and U.S. Pat. No. 5,056,912. This liquid crystal display element includes metal wiring for electrodes of each picture element, nonlinear elements or switching elements added as means for controlling the individual picture elements, and portions (light shielding portions) not contributing to the display such as the gaps around the electrodes of each picture element. Thus, particularly in this transmission-type liquid crystal display element, the light arrived at the light shielding portions as a part of the light which is emitted from a light source and irradiated on the liquid crystal display element is not transmitted through the liquid crystal display element, and therefore reduces the light-utilization efficiency. This light-utilization efficiency is normally expressed by the aperture ratio of the liquid crystal display element. It is important to increase this aperture ratio. The aperture ratio is defined as follows. EQU Aperture ratio=(Effective area contributing to the display at one picture element)/(Area of all region of one picture element)
In addition, when the liquid crystal display element is small-sized for a compact display using the liquid crystal display element, the area of one picture element is reduced more as the liquid crystal display element is small-sized, provided that the number of picture elements of the liquid crystal display element is constant. Thus, the effect of the light-shielding portions becomes great, and it is difficult to increase the light intensity. Moreover, in order to increase the definition of the liquid crystal display element with the same size and thereby to increase the resolution of the liquid crystal display using the liquid crystal display element, it is necessary to reduce the pitch of the picture elements. In that case, if all the constituents of the liquid crystal display element can be reduced analogically, the effect of the light-shielding portions are not changed, and the aperture ratio is not changed. However, the width of the metal wiring of electrodes and size of additional devices cannot be reduced to a certain value or below from the viewpoint of etching precision and alignment precision. As a result, the aperture ratio is decreased with the increase of the definition.
Examples of a transmission-type liquid crystal display element improved in the aperture ratio and liquid crystal display using this liquid crystal display element are described in, for example, Japanese Patent Laid-open Gazettes No.60-165622 and No.61-11788 in which the liquid crystal display element has a micro-lens array provided.
In either one of the above conventional examples, each unit lens portion of the micro-lens array is a circular lens or a semi-circular cylindrical lenticular lens. Each picture element of the above liquid crystal display element is normally of a square shape or rectangular shape. Therefore, when the micro-lens array (circular) is provided on the liquid crystal display element (square or rectangular), the light incident on the aperture area of each unit lens portion of the micro-lens array can be converged on the aperture area of the liquid crystal display element, but the light incident on the other area is incident to the light-shielding portions. Thus, all the incident light cannot effectively enter each unit lens portion, and as a result the improvement of the aperture ratio is limited.
Moreover, the liquid crystal display element has generally a large dependency on the visual angle. The liquid crystal display element can exhibit good characteristics for the viewers when it is looked up at an angle relative to the direction perpendicular to the display screen. Thus, when the liquid crystal display element is disposed to be tilted relative to the incident light, the incident light to the micro-lens array of the conventional liquid crystal display element is not converged just at the aperture area of the liquid crystal display element.
Also, in the display using the liquid crystal display element with the micro-lens array and an illumination optical system or in the projection-type display using a screen on which the image on the liquid crystal display element is projected through a projection lens, the aperture ratio improvement effect of the liquid crystal display element with the micro-lens array is changed by the illumination optical system. However, this is not considered in the above conventional liquid crystal display element and display using the same.